The present invention relates to a novel process for the preparation of lithium metaphosphate (LiPO3) by a solid state thermal reaction. This compound is useful as an intermediate for the preparation of lithium hexa fluorophosphates (LiPF6). This salt is a good electrolyte in aqueous, non-aqueous, solid and selected polymer medium. The present invention particularly relates to the preparation of lithium metaphosphate (LiPO3) compound which is the basic chemical for the preparation of lithium hexafluorophosphates (LiPF6) by a novel solid state method which is not hitherto attempted anywhere.
Prior art literature on lithium metaphosphate (LiPO3) discloses the reaction of lithium salts with metaphosphoric acid, which is obtained by heating pyro-phosphoric acid or ortho-phosphoric acid. The reaction occurring for the above two thermal processes are as follows:
Advanced Inorganic Chemistry, S. Sathiya Prakash G. D. Tuli, S. K. Basu and R. D. Radan, S. Chand and Co., New Delhi, p. 988 (1998).
The above methods need controlled conditions for the preparation of lithium metaphosphate. The above methods for the preparation of lithium metaphosphate also suffer from the following disadvantages:
1. More than one step is involved to prepare LiPO3.
2. Needs crystallization procedure once the product is formed from aqueous solution.
The main object of this present invention is to provide a simple novel process for the synthesis of lithium meta phosphate (LiPO3) which obviates the draw back mentioned above.
Another object of the present invention is to provide a complete solid state reaction procedure for the preparation of LiPO3.
Another object of the invention is to provide a single step process to obtain LiPO3.
Yet another object of the invention is to get high yield of the product LiPO3 ( greater than 90%).
The above and other objects have been achieved by the solid state method for the preparation of lithium metaphosphate of the invention.
Accordingly, the present invention provides a process for the preparation of lithium metaphosphate comprising reacting a lithium source and a phosphorous source in a ratio of 1:1-2 in solid state at a temperature in the range of 300 to 650xc2x0 C. to obtain the desired lithium metaphosphate.
In one embodiment of the invention, the lithium source is selected from the group consisting of Li2O, LiCO3, LiOH, LiNO3 and any mixture thereof.
In another embodiment of the invention, the phosphorous source is selected from the group consisting of ammonium pyrophosphate, ammonium orthophosphate, diammonium hydrogen phosphate and ammonium dihydrogen phosphate and any mixture thereof.
In another embodiment of the invention, the reaction is carried out in solid state in a single step.
In yet another embodiment of the invention, the reaction is carried out at a temperature of 350xc2x0 C. for a time period of 12 hours and the lithium source is selected from Li2O, LiOH and LiNO3.
In another embodiment of the invention, the reactive materials are heated in a muffle or in an electric furnace.
In yet another embodiment of the invention, Li2CO3 is reacted with the phosphorous source at a temperature of 600xc2x0 C.
In another embodiment the lithium source and the phosphorous source are mixed and ground well before being heated.
In another embodiment of the invention, the lithium source and the phosphorous source are mixed in an equimolar ratio.